A typical conventional two-stage Miller compensated amplifier system relies on directly coupling the outputs of the first stage with the inputs of the second stage. The result is that the headroom or signal swing of the second stage is limited by the output common mode voltage of the first stage. This is undesirable in many designs where a maximum swing is needed to achieve a high signal-to-noise ratio (SNR).
One conventional two-stage Miller compensated amplifier system attempts to improve this problem by utilizing a wide swing output stage. This results in outputs of the second stage being able to swing within one VDSAT of the rails. However, this limits the output common mode voltage of the first stage to one VGS above ground due to the direct connection of the first stage outputs with the inputs of the second stage. The result is the headroom and input compliance of the first stage is severely restricted, especially if current source devices are used.